The SIM card is also referred to as a smart card, or a user identity card, and a digital mobile terminal must be installed with the card for use. The SIM card stores contents such as information of clients of digital mobile telephones, encrypted keys, and telephone books of users etc. on a computer chip, for use by the GSM network to authenticate identities of clients, and encrypt the voice information during a call of the client.
With the development of mobile communications, different companies design SIM cards with different sizes, for example, an ordinary SIM card and a Micro SIM card etc., so that users will not easily change cards, so as to lock more users. However, due to different sizes of the SIM cards, requirements for user experiences are limited.